1. Field of the Invention
The present invention relates to an outboard motor and a watercraft including the same, and specifically to an outboard motor including a V-shaped 4-cycle engine which includes a fuel injection device that directly injects fuel into a combustion chamber.
2. Description of the Related Art
Conventionally, as described in JP 2003-74340, a 4-cycle engine including a fuel injection device for injecting fuel into an intake port of an outboard motor (hereinafter, such a fuel injection device will be referred to as an “in-port injection device”) is used as an engine of an outboard motor. Since the pressure in the intake port is lower than the pressure in the combustion chamber, the injection pressure of the in-port injection device may be relatively low. Therefore, a pump having a low ejection pressure may be used as a fuel pump for supplying fuel to the in-port injection device. As such a fuel pump, a compact pump or an electric pump is usable. Thus, this type of engine has a high degree of freedom for layout of the fuel pump.
Meanwhile, in order to improve the fuel efficiency and performance, it has recently been studied to adopt a V-shaped 4-cycle engine including a fuel injection device for directly injecting fuel into a combustion chamber (hereinafter, such a fuel injection device will be referred to as an “in-cylinder combustion device”). JP 2002-138925 describes such an engine.
The engine described in JP 2002-138925 includes a left bank extending in an obliquely rearward and leftward direction and a right bank extending in an obliquely rearward and rightward direction. In a cylinder head in the left bank, an exhaust port and an intake port located to the left of the exhaust port are formed. In a cylinder head in the right bank, an exhaust port and an intake port located to the right of the exhaust port are formed. In other words, the exhaust ports are located at an inner position in a width direction of the outboard motor, and the intake ports are located at an outer position in the width direction of the outboard motor. Hereinafter, unless otherwise specified, the term “width direction” refers to the width direction of an outboard motor, and the expressions “inward in the width direction” and “outward in the width direction” respectively refer to inward and outward in the width direction of the outboard motor.
Each intake port is connected to an intake path for introducing air into the intake port. The intake ports and the intake paths each extend from the combustion chamber in an obliquely rearward and outward direction and then are largely curved in a forward direction at an outer portion in the width direction of the corresponding bank. The fuel injection device is attached to a portion of the cylinder head which is outward in the width direction.
In the engine described in JP 2002-138925, each intake port is largely curved in a portion of the cylinder head which is outward in the width direction. This causes a problem that air is unlikely to flow smoothly in the intake port and thus the combustion chamber is unlikely to be filled with a sufficient amount of air. As a result, the effect of, for example, improving the engine output, which would be provided by directly injecting fuel into the combustion chamber, may not be sufficiently achieved.
In order to smooth the flow of the air in the intake port, it is conceived to curve the intake port more slowly. However, the fuel injection device is provided in a portion of the cylinder head which is outward in the width direction, and the presence of the fuel injection device may restrict the layout of the intake port. Because of the layout of the fuel injection device, the intake port may not be curved more slowly. In addition, if the intake port is curved more slowly, the intake path may largely protrude outward in the width direction. This causes a problem that the size of the outboard motor in the width direction is increased.
Since the pressure in the combustion chamber is higher than the pressure in the intake port, the injection pressure of the in-cylinder combustion device needs to set high. For this reason, a fuel pump for supplying fuel to the in-cylinder combustion device needs to have a high ejection pressure. As such a fuel pump, a relatively large pump drivable by a cam shaft of the engine is preferably usable. However, such a large fuel pump needs to be located close to the cam shaft and also requires a large space for installation.
In an outboard motor including a V-shaped engine, portions corresponding to the outermost portions of the left bank and the right bank in the width direction of the outboard motor are of the largest width. From the viewpoint of suppressing an increase of the width of the outboard motor, it is preferable that the portions corresponding to the outermost portions of the left bank and the right bank are as compact as possible. However, the outboard motor described in JP 2002-138925 includes the fuel pump in the portion corresponding to the outermost portion of the left bank. This causes a problem that the width of the outboard motor is increased.